1. Field of the Invention
The present invention discloses a well safety system with two surface controlled subsurface safety valves.
2. Description of Related Art
Gas storage wells are frequently located in depleted hydrocarbon reservoirs at a relatively shallow depth less than five thousand feet. Common characteristics of gas storage wells are relatively low flowing pressures, less than three thousand psi, a large unrestricted flow area and high flow rates with frequent variations in the flow. Examples of subsurface safety valves particularly adapted for use in gas storage wells are shown in U.S. Pat. Nos. 3,481,362; 3,459,260; and 3,491,831. Each of these patents was invented by William W. Dollison and assigned to Otis Engineering Corporation.
Well safety systems with two downhole safety valves have been used from time to time. An example of such a two valve system is shown in U.S. Pat. No. 4,469,179. Normally well safety systems have only one downhole valve, either a direct acting safety valve such as shown in U.S. Pat. No. 4,339,001 or a surface controlled subsurface safety valve such as shown in U.S. Pat. No. 4,201,363.
Subsurface safety valves typically have either a ball, flapper, or poppet type valve closure mechanism as shown in U.S. Pat. No. 3,860,066. However, downhole valves with sliding sleeve type valve closures are known. U.S. Pat. No. 4,624,310 discloses a well safety system with a vent valve that has several characteristics in common with the annulus flow safety valve of the present invention.
The alternative flow paths provided by this invention are similar in some respects to downhole safety systems having "block and kill" valves. An example of such a safety system is shown in U.S. Pat. No. 4,566,478 invented by Thomas M. Deaton.
The above referenced patents are incorporated by reference for all purposes within this application.